The QCD axion is one of the most motivated scenarios beyond the Standard Model. This simple extension not only explains in an elegant way the absence of CP violation in the strong interactions [1]}, [2]} but could also account for the Dark matter abundance [3]}, [4]}, [5]}. Furthermore, the QCD axion is a highly predictive scenario since a lot of the properties of this pseudoscalar stem from its pseudo-Goldstone boson nature: both the axion mass
and the couplings to ordinary matter scale as \(1/f_a\) , where \(f_a\)  is the
axion decay constant, denoting the scale at which the Peccei-Quinn (PQ) symmetry \(U(1)_{\rm PQ}\)  is spontaneously broken.
